I got my new Nikon camera about two months ago and just a few days ago, i realized that i don’t know everything about the auto focusing system on it. So i set out to learn everything there is to know and i will share it here with whoever wants to learn. My camera is a D7100, but most modern Nikon DSLRs will be similar and most of it is general, so please keep reading even if you’re using a D90, a D5200 or any other model.
How to control the auto focus
Let’s get this out of the way first. You control the auto focus by pressing the shutter button half way down. There is a different and very useful way to focus, that i’ll tell you about at the end of this post.
Different focusing modes
The camera has three different focusing modes: single, continuous and auto. It is very important to understand what they are and when to use which mode, because they’re very different and they should be used it different situations. You change between these modes by pressing your AF button and rotating your primary selection wheel, the one on the back.
In your display, you will see the letters “AFS”, “AFC” or “AFA” for single, continuous and auto. If you look in your viewfinder, you’ll see the same letters as long as the AF button is pressed. Here’s how each of them works:
Auto focus single – AFS
When you’re in auto focus single mode, your camera will focus once when you press your shutter button halfway and hold that focus until you press it halfway again. This mode is typically used for stationary subjects and people who don’t move a lot. When you’re in single mode, you’ll often be using the “focus and recompose” technique, which i’ll explain later in this post.
One thing that’s important to understand, is that in this mode, the camera will not let you take a picture if your subject is not in focus. If you press the shutter button when the camera can not find focus on the subject, nothing will happen. This will occur sometimes if your subject has very little structure or in low light situations.
Auto focus continuous – AFC
When in continuous mode, the camera will be focusing all the time when your shutter button is pressed halfway. This mode is best for moving subjects, such as kids or pets playing or sports. If you want to lock your focus when you’re in this mode, you can do that by pressing the AE-L/AF-L button, which locks the focus (and the exposure if you have your camera set to up that way).
Auto focus auto – AFA
When you’re in auto focus auto mode, your camera will use its built in logic to analyze your subject and pick single or continuous mode depending on your subject. This mode is good to use before you have a good understanding of the two other modes, but i recommend that you get a solid understanding of the focus modes and use your own judgement to decide by yourself which one to use.
The camera will indicate which focus points are used. You’ll see this as one or more of the focus squares in your viewfinder blinking red. It will also indicate that it has focus by showing a small white circle in the lower left part of the viewfinder, just left of the shutter time. Switch to continuous mode (AFC) and press the shutter button halfway as you move your camera. You’ll see the focus indicator blinking as the camera focuses over and over. In single mode (AFS), you’ll see it focus once and the indicator says on for as long as you keep the button pressed halfway.
Depending on what camera you have, this will look a little different. On the Nikon D7100, there are 51 auto focusing points, spread over the image area. It looks something like this:
You can choose different sizes of groups of focusing points and two special modes:
- 9 points
- 21 points
- 51 points
Choosing the focusing area is done by pressing your AF button and rotating your front selection wheel. The display will say “S”, “d 9″, “d21″, “d51″, “3D” or “auto”.
Typically, you should be using the single focusing point most of the time. You point it where you want to focus, press the shutter button halfway and the camera will focus there. If you want, you can move the focus point, or group of focus points, around using the multi-directional pad (d-pad) on the back of your camera.
When you’re in 9-, 21- or 51-point mode, you’re telling the camera how far from the center auto focus point it can look for focus if it loses focus in the center point. You’ll notice that even if you’re in 9-, 21-, or 51-point mode, you will still only see the center focus point in your viewfinder. Using the d-pad, you move the entire focus point group around.
One important tip – pressing the button in the center of your d-pad will reset your focus point to the center if you’ve moved it. If you want to avoid resetting it or accidentally moving it, switch to locked mode – “L” (as in the image of the d-pad above).
I have to admit i have never used this mode. Theoretically, it should be useful when you shoot sports. The camera will focus on a moving subject and calculate its path and switch focus points to keep focusing on the moving subject. I suspect this requires a fairly simple situation with a single moving subject. I will give it a try next time i shoot a handball game and tell you what i find out.
In auto mode, the camera will simply focus on whatever focusing point is the closest. This is not always what you want. Learn about the other modes and use them and your images will be so much better. It’s not that complicated.
Focus and recompose
When you’re in single focus mode, you have two choices: either you can move your selected focus point to the part of the viewfinder where you want the focus to be by using the d-pad or you can point your currently selected focus point to where you want the camera to focus, press the shutter button halfway and then recompose and shoot the picture. The latter is of course much faster and usually the best way to go. If you look at a professional press photographer, you see them doing this all the time. It looks like they’re wiggling their camera back and forth.
These images will explain this. Let’s say your center focus point is selected. You want the orange to be in focus and you want it to the left in the picture. You point your focus point at the orange and press the shutter button halfway. You will see the focus indicator, the little white circle, in your viewfinder.
Now you move, while holding your shutter pressed halfway, turn your camera so that the orange is to the left. When your composition is the way you want it, you press your button to take the picture.
Back button focus
This is a different way to control the focus on your camera that i sometimes use when i have my camera mounted on a tripod. Some photographers use it all the time. You can set your AE-L/AF-L button to “AF ON”, which means you move the focusing from the shutter button halfway press to the AE-L/AF-L button, which you control with your right thumb on the back of the camera.
To set your auto focus up this way, open up menu and go to “Custom settings menu”->”Autofocus”->”Assign AE-L/AF-L button” (menu option f4). This menu has an option named “AF-ON” which activates back button focusing.
To return to normal focusing, simply go back to the same menu and choose the top option – “AE/AF lock”.
Of course, you can choose to switch to manual focus. Turn the lever under the AF button to “M” and auto focus is disabled so that you can use the focus ring on your lens to focus manually.